CherryTree - A hierarchical note taking application, featuring rich text and syntax highlighting, storing data in a single xml or sqlite file.
Raneto - Open source, flat-file Knowledgebase platform that uses static Markdown files
Cryptee - Cryptee is a safety and privacy focused, encrypted and cross-platform personal data storage service. You can write personal documents, notes, journals, store photos and all sorts of other files.
HowHive - Knowledgebases for teams and companies of all sizes. Knowledge sharing and finding made simple.
Lastpass - LastPass is an online password manager and form filler that makes web browsing easier and more secure.
Obsidian.md - A second brain, for you, forever. Obsidian is a powerful knowledge base that works on top of a local folder of plain text Markdown files.